1. Field of the Invention
This invention relates to alkyl-substituted polyarylethers and to their use in an improved method of making high molecular weight polyarylethers.
2. Background
Polyarylethers comprise a class of organic polymers having etheric oxygen valently connecting aromatic nuclei or residua of aromatic compounds. As the term is used herein, a polyarylether consists of three or more aryl ether repeat units, --Ar--O--, wherein Ar may be a mono- or polynuclear aromatic compound. Many polyarylethers are characterized by high use temperatures, thermal and photochemical stability and resistance to attack by a variety of solvents. These desirable properties are due in part to the crystalline nature of the polymers and to their high melt temperatures. Unfortunately, the highly crystalline nature of many of the polyarylethers also make them difficult to prepare at the high molecular weights necessary for toughness. This problem is especially acute for polyarylether ketones containing repeat units I and II: ##STR1##
A number of methods, including nucleophilic aromatic displacement polycondensations and Friedel-Crafts polycondensations, have been developed for the synthesis of polyarylethers, polyarylether ketones and related polymers.
Johnson, et al., U.S. Pat. No. 4,108,837, disclose polyarylene polyethers which are linear thermoplastic reaction products of an alkali metal double salt of a dihydric phenol and a dihalobenzenoid compound.
Johnson, et al., J. Polymer Sci. Part A-1, 5 (1967), 2375-2398, disclose a crystalline polyarylether ketone-containing repeat unit II (supra) and having a melt temperature T.sub.m of 350.degree. C. No direct evidence is presented concerning the molecular weight of this polymer, but it is stated that the crystallizable polyethers tend to be brittle (unstretched) unless obtained in the amorphous form. This brittleness may result from the polymer having a low molecular weight.
Rose, U.S. Pat. No. 4,010,147, discloses the use of certain diaryl sulphones as solvents in the preparation of high molecular weight polyarylether ketones by the reaction, at 250.degree. to 400.degree. C., of a dialkali metal salt of a bisphenol which contains ketone linking groups and a dihalobenzenoid compound having halogen atoms activated by a ketone or sulphone linking group.
Rose, et al., U.S. Pat. No. 4,320,224, disclose a tough crystalline thermoplastic aromatic polyether ketone containing the repeat unit II (supra), alone or in conjunction with other repeat units, said polymer having an inherent viscosity of at least 0.7. The process disclosed for preparing these high molecular weight polymers involves the use of elevated reaction temperatures and high boiling solvents.
Marks, U.S. Pat. No. 3,441,538, discloses preparations of very high molecular weight polyarylether ketones having repeat unit I (supra) and polyarylether sulfones, using a mixed BF.sub.3 /HF catalyst and, for example, p-phenoxybenzoyl chloride or p-phenoxybenzene sulfonyl chloride Friedel-Crafts (BF.sub.3 /HF-catalyzed) reactions to prepare other polyarylether ketones are also disclosed. Dahl, U.S. Pat. No. 3,953,400, discloses a modified BF.sub.3 /HF process employing end-capping reagents to control the inherent viscosity at 0.8-1.65.
Kelsey, EPO No. 148,633, discloses a modified nucleophilic aromatic displacement polycondensation process for preparing high molecular weight crystalline polyarylether ketones by first forming a high molecular weight amorphous polyketal ketone under mild conditions, and then converting the polyketal ketone to crystalline polyarylether ketone by acidic hydrolysis. It is not possible, however, to form a polymer with repeat unit II (supra) by this method.
Walton, "Protective Groups in Organic Chemistry", Ch. 1, pp 23-25, J. F. W. McOmie (ed.), Plenum Press, New York, 1973, reviews the use of t-butyl and i-propyl substituents as protective groups in organic synthesis, and methods for their removal from aromatic rings. Transalkylation procedures using benzene/AlCl.sub.3, m-xylene/HF or p-toluenesulfonic acid/CO.sub.2 are said to be fairly specific for t-butyl transfer. Chlorobenzene/AlCl.sub.3 will remove the i-propyl group from o-isopropylphenol.
Kruse, et al., U.S. Pat. No. 4,487,978, disclose the use of strong Lewis acids (sulfonic acids) and alkylbenzenes at 100.degree. -200.degree. C. to dealkylate bisphenols substituted with C.sub.4-8 t-alkyl groups wherein the quaternary carbon atom of the t-alkyl group is directly attached to the aromatic ring.
Olah, et al., Synthesis, 1986, pp 513-531, especially p 518, disclose the use of Nafion.RTM.-H to dealkylate 2,6-di-t-butyl-p-cresol to o-cresol at about 60.degree. C. Nafion.RTM.-H is the acidic form of a solid, superacidic, perfluorinated resin-sulfonic acid catalyst film or powder (available from Aldrich Chemical Company, Inc.). It is noted that toluene is a better acceptor than benzene.
Neither Kruse, et al. nor Olah, et al. suggest the use of strong acid catalysts to remove alkyl groups from alkyl-substituted polymers.
Reske, et al., U.S. Pat. No. 3,770,669 and 3,792,148, disclose a process for making shaped articles from polyamides which are high-melting or sparingly soluble or exhibit both properties, which process comprises molding N-alkyl substituted polyamides from the melt or from solution and then thermally splitting off the substitutents as unsaturated hydrocarbons. Particularly preferred substitutents are n-propyl, i-propyl, i-butyl and t-butyl groups.
Mohanty, et al., 31st International SAMPE Symposium, Apr. 7-10, 1986 Preprints, pp 945-955, disclose the synthesis of an amorphous high molecular weight copolymer from hydroquinone, t-butyl hydroquinone and 4,4,-difluorobenzophenone. The copolymer is subsequently partially dealkylated with aluminum trichloride in chlorobenzene to yield a semicrystalline material. No method is disclosed for the complete dealkylation of the copolymer.
European Patent Application Publication No. 0,157,732 discloses a copolymer having repeat units of the formulas ##STR2## wherein X is a diradical which includes --SO.sub.2 -- and --CO--,
Y is an aryl diradical which includes ##STR3## R.sub.3 is halogen, C.sub.1-4 alkyl, or C.sub.1-4 alkoxy, and m is 0 or 1 to 4. PA1 (i) at least one alkyl-substituted dihydric phenol; and PA1 (ii) an aromatic dihalide having at least one, inert, halogen-activating, electron-withdrawing group in the positions ortho and para to the halogen atoms on the aromatic ring,
Deckers, DE No. 3,342,433, discloses the use of mixtures of carbonates of Li and/or alkaline earths with carbonates of Na, K, Rb, and/or Cs in the preparation of aromatic polyethers by nucleophilic polycondensation. For example, a mixture of CaCO.sub.3 (10.0 g) and K.sub.2 CO.sub.3 (1.4 g) was used in the reaction of 4,4'-difluorobenzophenone (21.8 g), hydroquinone (11.0 g), 4-chlorodiphenyl sulfone (0.10 g), diphenyl sulfone to give a polyether with relative viscosity 4.42 dL/g. In contrast, a polyether with relative viscosity 1.64 dL/g was obtained when K.sub.2 CO.sub.3 (15.1 g) was the only carbonate used.